2006 Annual Report 4d.Progress report. This report serves to document research conducted under a Specific Cooperative Agreement between ARS and Mississippi State University. Additional details of research can be found in the report for the inhouse project 6406-32000-008-00D, Diagnosis and Control of Mycoplasmosis in Poultry. Results have shown that commercial Single Combed White Leghorn chickens, housed in biological isolation units, experienced delays in onset of lay and in production of undersized eggs after being inoculated at 12 weeks of age with F-strain Mycoplasma gallisepticum (FMG). These data further showed that these alterations in performance and egg characteristics are related to mutual functional disturbances in the liver, ovary, and oviduct, changes in yolk composition, and changes in blood hematocrit.